This master's thesis deals with the influence of the exothermic riser sleeves on the solidification time of aluminum alloys. The thesis is divided into five parts. The first chapter describes solidification of cast alloys. The second chapter deals with the designing of risers. The third chapter is focused on the types of risers. The fourth chapter describes ways of intensification of risers and chemical composition of exothermic and insulating mixtures for production of riser sleeves. The main fifth chapter focuses on experimental measurements of temperatures and solidification time of aluminum alloy in castings, risers and exothermic and insulating riser sleeves.

Riser sleeve thermophysical properties for simulation are developed using an inverse modeling technique. Casting experiments using riser sleeves are performed in order to measure temperatures in the liquid steel, the riser sleeve, and the sand mold. Simulations are created and designed to replicate the casting experiments. Riser sleeve material thermophysical properties are iteratively modified until agreement is achieved between the simulation and the measured data. Analyses of sleeve material performance are carried out using the developed thermophysical properties. The modulus extension factor (MEF) is used to quantify sleeve performance and is determined for all riser sleeve materials studied here. Values are found to range from 1.07 to 1.27. A sleeve material's effects on casting yield are shown to depend only on the MEF and therefore a sleeve's exothermic or insulating properties serve only to increase the overall quality of the sleeve, expressed by the MEF, and do not independently affect the casting yield at any casting size studied here. The use of riser sleeves is shown to increase the maximum yield up to 40% for chunky castings, however increases of only 8% are observed for very rangy castings. Riser sleeve thickness is shown to be extremely influential on casting yield. Scaling the sleeve thickness by the riser diameter shows that, for a typical sleeve, an optimum riser sleeve thickness is 0.2 times the riser diameter for chunky castings. A scaled sleeve thickness of 0.1 is found to be an optimum sleeve thickness for very rangy castings. Below a scaled sleeve thickness of 0.1 sleeve performance is found to be highly sub-optimal.